This invention relates to a sorter in which pins secured to and projecting horizontally outwards from opposite sides of bin trays are engaged in spiral guide surfaces defined in upstanding cylinders and a stack of bin trays are shifted upwards and downwards by drivingly rotating the cylinders.
Conventionally, there have been known sorters having the following construction. A spiral groove is defined on the surface of each of two upstanding cylinders arranged sideways. Pins secured to opposite sides of a plurality of bin trays disposed between the two cylinders are respectively engaged with these grooves. The cylinders are rotated by means of a motor, and thereby the bin trays are shifted upwards or downwards by causing the pins to slide relatively along guide surfaces formed by the grooves.
There have also known sorters provided with a sheet processing device including a stapler and a punch. In the sorters provided with the sheet processing device, a notch is formed in each rear end portion of a plurality of bin trays, and processing is applied to sheets placed on a given bin tray by moving the sheet processing device up to the notch of this bin tray.
In the sorter provided with the movable sheet processing device, it is required that the sheet processing device be moved to the bin tray bearing the sheets to be processed. However, since the sheet processing device is relatively heavy, it is required to improve rigidity of a mechanism for moving the sheet processing device and to increase power of a motor for driving the moving mechanism. These requirements have resulted in a complicated construction of the sheet processing device.
In order to solve the above problem, it is preferable to move the relatively light-weighted bin tray toward the sheet processing device. However, there has existed no such sorter provided with a mechanism for moving the bin tray, and accordingly it is necessary to consider a specific construction for the bin moving mechanism.
This bin moving mechanism necessitates a construction for disengaging pins of the bin tray bearing sheets to be processed from the grooves of the cylinders and moving the same toward the sheet processing device along guide members. In this case, it is necessary to smoothly transfer the pins of the bin tray from the grooves of the cylinders to the guide members. Unless otherwise, problems will occur such as misalignment of sheets placed on the bin tray.
On the other hand, the inertial force is acting on the cylinders and a rotatable shaft of a motor for rotating the cylinders. Accordingly, even if the braking force is applied to the rotating cylinders, the cylinders still rotate to some degree. Further, a rotating amount of the cylinders after application of the braking force due to the inertial force varies according to the weight of copy sheets placed on the bin trays. A drive transmission mechanism including gears and a timing belt for transmitting the torque of the motor to the cylinders are invariably associated with backlash. In order to accurately stop rotation of the cylinders in a predetermined position where, for example, the pins of the bin tray are smoothly transferable to the guide members, it is necessary to eliminate influence of the inertial force and backlash of the drive transmission mechanism.
Moreover, in the above sorter, the frictional resistance acts between the pins and grooves and between the pins and guide members. The frictional resistance particularly increases in the case where the bin trays are shifted upwards or the weight of the copy sheets on the bin trays are heavy. Such increased frictional resistance becomes a hindrance to smooth sliding of the bin tray and also produces frictional sounds. Further, the frictional resistance gives an increased burden on the motor for driving the cylinders, and abrades the pins and grooves. Accordingly, it is necessary to reduce the frictional resistance.